Sakis, thats all fine and dandy, but the amp still works when I heat up the "Diode Transistor array(s)" which is also known as a Varistor. or at least reffered to as one, you might be thinking of a slightly older model. I have the bottom off, and I've bypassed and re-attatched these myself, if they are not actually there, then I guess I need to search for ghosts instead of amp problems...
Charging the cam battery, I'll post pics after work tonight. schematics are above as well for refference, D19 and D20 are the 2 diode arrays in question, they mount to the bottom of the heatsink.
but I don't think they are the problem anymore, I do agree that it's probably the caps, my problem right now is the Big caps are 50V 8000uf, I searched high and low for these as well.
I kind of figured since once it's warmed up it runs no problem, that it would have to be something attached to the heatsink, but I'm in agreement with the ideal that it would be the small caps...
Biggest problem I have with that is, I have no resources to start ordering parts, here in canada, I checked out digi-key, they lack many of the parts I need.
but I don't think they are the problem anymore, I do agree that it's probably the caps, my problem right now is the Big caps are 50V 8000uf, I searched high and low for these as well.
I kind of figured since once it's warmed up it runs no problem, that it would have to be something attached to the heatsink, but I'm in agreement with the ideal that it would be the small caps...
Biggest problem I have with that is, I have no resources to start ordering parts, here in canada, I checked out digi-key, they lack many of the parts I need.
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stv3 is just 3 diodes in series for thermal regulation of output bias. (D19 and 20 in the schematic. Normally, I would look for problems in the protection circuit, but if you here the relay click, then it is probably OK. One possibility is low regulated (20v) supply - it feeds the input part of the power amp through a resistor (r299) and cap (C249 and is to prevent turn on thumps. Best way to trouble shoot is to use a scope and follow the signal. If no scope, then check the DC voltages coming out of the supply. The STV3 should have nothing to do with a turn on problem. Good luck.
Thank you sregor, I'll be going over the schematic again shortly to track them down and look over the board, I should have some spare goodies around to attempt a check.
50 volt is a pretty common rating but remember that it is just that, a maximum rating. since its not for protection (voltage wise) you can go higher. digikey should have that value for 63volt i just bought some 10kuf at that voltage two weeks ago.
Also you can try allied they ship (and price) for canadian dollars
thanks I kinda figured that, but wasn't sure about the whole rating system, my question next is how much can the uf change? the best I can find in a solder-able lead configuration is 63v @ 8200uf, at 5-7 bucks a pop on digi.
checking allied if I can find the site.
ok seem to have lost the ability to edit my posts, so correction, 50V 8200uf on digi, went on allied and they only have 63V 8200uf, so if the difference of 200uf isn't going to make a big boom, I think maybe I'll go with that if I decide to replace those caps.
it seems that i will have to skip this post since my saynig are nott understood ....
in the 30 or more years that i do electronics i found may be one or two cases that a diode aray like the one you posted was faulty and yes its a diode array not a varistor
to be more specific even if this network and related parts arround it are not working properly the amplifier will distort or overheat or blow fuses at start up but other than that will play music .... so again you are in the wrong direction ....you are chasing a ghost eventhough the solution is given to you
another serious point is that regarding the main caps you are talking for you you information if these caps are 95% dead your amplifier will still work will produce music but with extreme distortion and uncapable of power more than 2-3 watts .... it will still play .....
on the other hand if a signal capacitor is dryied out on the signal or feedback path the amp is dead .....
conclusion
it seems that you cannot do your homework, read the manual ,change a few f***cking small capacitors and go ahead with it ....
in the 30 or more years that i do electronics i found may be one or two cases that a diode aray like the one you posted was faulty and yes its a diode array not a varistor
to be more specific even if this network and related parts arround it are not working properly the amplifier will distort or overheat or blow fuses at start up but other than that will play music .... so again you are in the wrong direction ....you are chasing a ghost eventhough the solution is given to you
another serious point is that regarding the main caps you are talking for you you information if these caps are 95% dead your amplifier will still work will produce music but with extreme distortion and uncapable of power more than 2-3 watts .... it will still play .....
on the other hand if a signal capacitor is dryied out on the signal or feedback path the amp is dead .....
conclusion
it seems that you cannot do your homework, read the manual ,change a few f***cking small capacitors and go ahead with it ....
I've obviously left out a few sentences above mysteriphys. It's safe to go up in voltage rating on your caps. its not always safe to go up in capacitance.
my point earlier was that 50volt is common but not as common as 63 volt.
and as sakis has said test your signal caps
my point earlier was that 50volt is common but not as common as 63 volt.
and as sakis has said test your signal caps
I'm doing the homework, by asking around, I apologize if I mis-understand, but I'm new to this, I can not just jump in and know where all of the problems are. the varistor is reffered to as a diode array, or vice versa according to what I read on-line they are the same thing.
I also now understand that nothing around them would be the issue, so there is no need to be upset that I'm not understanding you.
p.s. there is no distortion at any volume once the amp is heated up and operating. I'm going to try to swap some caps, but judging from what I've seen in the past, and personally done, I don't think they are an issue.
ok, my issue was that the only caps I can find that are the right uf aren't mounted by leads, so if I go to all the trouble of buying the 63v 8000uf I'm going to have to build and wire a seperate board to mount them on.
in the age of 14 i was allready repairing amplifiers of course my knowledge was very low my theory was cr***ap ( probably still is ) but i realy wanted to fix the machine learn from it listen from it and go ahead
often as was expected igot things not working , missed things, used wrong approach ,or miss the obvious then my approach was very simple.... Replace everything !!!! then it had to work ...
that is childish but some times helped a lot ....
often as was expected igot things not working , missed things, used wrong approach ,or miss the obvious then my approach was very simple.... Replace everything !!!! then it had to work ...
that is childish but some times helped a lot ....
I ordered a few screw terminal biggin's for the amp, I will eventually work my way through it, I guess it's just going to be a slow project until I get anymore money to put into it. $45 bucks usd (after shipping) to a company called tedss... only place I could find them in stock :-/ we'll see how it goes.
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Those STV-3H diodes are indeed referred to in the 70's manuals as 'varistors', but that is a poor description since they are in fact multijunction diodes and their operation is nothing like a varistor. Sakis is correct, in that these very rarely go bad, even after a catastrophic amp failure. They are there to regulate the bias current as the amp heats up and cools down, and cannot be removed from the circuit! If a lead breaks (or is intentionally desoldered), or the diode goes open, bias current goes to 'infinite' and the outputs blow up. If they go shorted, then you will not be able to get any bias current to flow, although the amp will still work...poorly.
Before you start replacing things, like big power supply caps that probably have nothing to do with the current failure, you need to get it running. If the speaker relay will not engage, then there are three major possibilities:
1. The protection circuitry, which is designed to monitor the DC output from both channels, is detecting too much DC on one or both channels and properly preventing the relay from closing.
2. There is a critical voltage missing that is causing excessive DC offset, or a missing voltage that is prevening the protection circuitry from functioning.
3. Third, and most likely (unless your poking around has made things worse), is that some old caps in the protection circuitry and a relay driver transistor with very low gain are preventing the protection circuitry from operating properly. I believe this to be the case, since heating the amp (and probably the relay driver transistor as a consequence) is causing the gain of this driver transistor to increase to the point that it eventually closes the relay. The transistor in question in this amp is Q21. Replace it and the rest of the small caps in the protection circuit, and you may have cured your issues.
Before you start replacing things, like big power supply caps that probably have nothing to do with the current failure, you need to get it running. If the speaker relay will not engage, then there are three major possibilities:
1. The protection circuitry, which is designed to monitor the DC output from both channels, is detecting too much DC on one or both channels and properly preventing the relay from closing.
2. There is a critical voltage missing that is causing excessive DC offset, or a missing voltage that is prevening the protection circuitry from functioning.
3. Third, and most likely (unless your poking around has made things worse), is that some old caps in the protection circuitry and a relay driver transistor with very low gain are preventing the protection circuitry from operating properly. I believe this to be the case, since heating the amp (and probably the relay driver transistor as a consequence) is causing the gain of this driver transistor to increase to the point that it eventually closes the relay. The transistor in question in this amp is Q21. Replace it and the rest of the small caps in the protection circuit, and you may have cured your issues.
Thanks EW, I'm happy to have your input on this, I've seen posts you've made around. I have to say, I understand they're not varistors, and I'm not argueing that they are that vs. the diode arrays. and at this point the point has been made.
aside from that, I'm going to track down the Q21 and see what I can find out. and I'll let you know how it goes, I do plan on upgrading/replacing all of the caps in this machine eventually, I've sidegraded this to a longterm project and I'm going to keep trying to learn more as I go along. if I get a working amp sooner, that's a bonus. but I enjoy the tinkering 🙂
I can't imagine anything I've done so far has made a large impact. I haven't had anything hooked to the input or output during my tests, and everything has been set to the off position aside from the power switch as well. speaker select has been off. though I'm not sure 100% since I know the outputs you speak of are before the speaker switch.
anyway, I'll post progress and results. I know it doesn't mean much considering most of you are looking for voltages but I can only do so much >.<.
hey, I know this goes back to another thread in another forum you've posted on already, is it going to be ok to put the BC637 Transistor in there as a replacement? there was some debate there, but I think he went with it anyway, just wondering what you think. thanks!
The gain of that BC637 isn't anything to write home about, and it's an EBC pin layout whereas the original 2SC1384 is ECB, and the solder holes for Q21 are lined up in a straight line, which makes installing the BC637 more difficult. If it were mine, I think I'd find a good part with a center-collector pin and more gain...but if you're careful and pay close attention, you can bend the leads around on that BC637 and make it work.
I'll look around again tonight, I'm still waiting for my t4's to come in, so I have time to research.
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